bump.c

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/*-------------------------------------------------------------------------
 *
 * bump.c
 *    Bump allocator definitions.
 *
 * Bump is a MemoryContext implementation designed for memory usages which
 * require allocating a large number of chunks, none of which ever need to be
 * pfree'd or realloc'd.  Chunks allocated by this context have no chunk header
 * and operations which ordinarily require looking at the chunk header cannot
 * be performed.  For example, pfree, realloc, GetMemoryChunkSpace and
 * GetMemoryChunkContext are all not possible with bump allocated chunks.  The
 * only way to release memory allocated by this context type is to reset or
 * delete the context.
 *
 * Portions Copyright (c) 2024-2025, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/backend/utils/mmgr/bump.c
 *
 *
 *  Bump is best suited to cases which require a large number of short-lived
 *  chunks where performance matters.  Because bump allocated chunks don't
 *  have a chunk header, it can fit more chunks on each block.  This means we
 *  can do more with less memory and fewer cache lines.  The reason it's best
 *  suited for short-lived usages of memory is that ideally, pointers to bump
 *  allocated chunks won't be visible to a large amount of code.  The more
 *  code that operates on memory allocated by this allocator, the more chances
 *  that some code will try to perform a pfree or one of the other operations
 *  which are made impossible due to the lack of chunk header.  In order to
 *  detect accidental usage of the various disallowed operations, we do add a
 *  MemoryChunk chunk header in MEMORY_CONTEXT_CHECKING builds and have the
 *  various disallowed functions raise an ERROR.
 *
 *  Allocations are MAXALIGNed.
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include "lib/ilist.h"
#include "port/pg_bitutils.h"
#include "utils/memdebug.h"
#include "utils/memutils.h"
#include "utils/memutils_memorychunk.h"
#include "utils/memutils_internal.h"
 
#define Bump_BLOCKHDRSZ MAXALIGN(sizeof(BumpBlock))
 
/* No chunk header unless built with MEMORY_CONTEXT_CHECKING */
#ifdef MEMORY_CONTEXT_CHECKING
#define Bump_CHUNKHDRSZ sizeof(MemoryChunk)
#else
#define Bump_CHUNKHDRSZ 0
#endif
 
#define Bump_CHUNK_FRACTION 8
 
/* The keeper block is allocated in the same allocation as the set */
#define KeeperBlock(set) ((BumpBlock *) ((char *) (set) + \
            MAXALIGN(sizeof(BumpContext))))
#define IsKeeperBlock(set, blk) (KeeperBlock(set) == (blk))
 
typedef struct BumpBlock BumpBlock; /* forward reference */
 
typedef struct BumpContext
{
    MemoryContextData header;   /* Standard memory-context fields */
 
    /* Bump context parameters */
    uint32      initBlockSize;  /* initial block size */
    uint32      maxBlockSize;   /* maximum block size */
    uint32      nextBlockSize;  /* next block size to allocate */
    uint32      allocChunkLimit;    /* effective chunk size limit */
 
    dlist_head  blocks;         /* list of blocks with the block currently
                                 * being filled at the head */
} BumpContext;
 
/*
 * BumpBlock
 *      BumpBlock is the unit of memory that is obtained by bump.c from
 *      malloc().  It contains zero or more allocations, which are the
 *      units requested by palloc().
 */
struct BumpBlock
{
    dlist_node  node;           /* doubly-linked list of blocks */
#ifdef MEMORY_CONTEXT_CHECKING
    BumpContext *context;       /* pointer back to the owning context */
#endif
    char       *freeptr;        /* start of free space in this block */
    char       *endptr;         /* end of space in this block */
};
 
/*
 * BumpIsValid
 *      True iff set is valid bump context.
 */
#define BumpIsValid(set) \
    (PointerIsValid(set) && IsA(set, BumpContext))
 
/*
 * We always store external chunks on a dedicated block.  This makes fetching
 * the block from an external chunk easy since it's always the first and only
 * chunk on the block.
 */
#define ExternalChunkGetBlock(chunk) \
    (BumpBlock *) ((char *) chunk - Bump_BLOCKHDRSZ)
 
/* Inlined helper functions */
static inline void BumpBlockInit(BumpContext *context, BumpBlock *block,
                                 Size blksize);
static inline bool BumpBlockIsEmpty(BumpBlock *block);
static inline void BumpBlockMarkEmpty(BumpBlock *block);
static inline Size BumpBlockFreeBytes(BumpBlock *block);
static inline void BumpBlockFree(BumpContext *set, BumpBlock *block);
 
 
/*
* BumpContextCreate
*       Create a new Bump context.
*
* parent: parent context, or NULL if top-level context
* name: name of context (must be statically allocated)
* minContextSize: minimum context size
* initBlockSize: initial allocation block size
* maxBlockSize: maximum allocation block size
*/
MemoryContext
BumpContextCreate(MemoryContext parent, const char *name, Size minContextSize,
                  Size initBlockSize, Size maxBlockSize)
{
    Size        firstBlockSize;
    Size        allocSize;
    BumpContext *set;
    BumpBlock  *block;
 
    /* ensure MemoryChunk's size is properly maxaligned */
    StaticAssertDecl(Bump_CHUNKHDRSZ == MAXALIGN(Bump_CHUNKHDRSZ),
                     "sizeof(MemoryChunk) is not maxaligned");
 
    /*
     * First, validate allocation parameters.  Asserts seem sufficient because
     * nobody varies their parameters at runtime.  We somewhat arbitrarily
     * enforce a minimum 1K block size.  We restrict the maximum block size to
     * MEMORYCHUNK_MAX_BLOCKOFFSET as MemoryChunks are limited to this in
     * regards to addressing the offset between the chunk and the block that
     * the chunk is stored on.  We would be unable to store the offset between
     * the chunk and block for any chunks that were beyond
     * MEMORYCHUNK_MAX_BLOCKOFFSET bytes into the block if the block was to be
     * larger than this.
     */
    Assert(initBlockSize == MAXALIGN(initBlockSize) &&
           initBlockSize >= 1024);
    Assert(maxBlockSize == MAXALIGN(maxBlockSize) &&
           maxBlockSize >= initBlockSize &&
           AllocHugeSizeIsValid(maxBlockSize)); /* must be safe to double */
    Assert(minContextSize == 0 ||
           (minContextSize == MAXALIGN(minContextSize) &&
            minContextSize >= 1024 &&
            minContextSize <= maxBlockSize));
    Assert(maxBlockSize <= MEMORYCHUNK_MAX_BLOCKOFFSET);
 
    /* Determine size of initial block */
    allocSize = MAXALIGN(sizeof(BumpContext)) + Bump_BLOCKHDRSZ +
        Bump_CHUNKHDRSZ;
    if (minContextSize != 0)
        allocSize = Max(allocSize, minContextSize);
    else
        allocSize = Max(allocSize, initBlockSize);
 
    /*
     * Allocate the initial block.  Unlike other bump.c blocks, it starts with
     * the context header and its block header follows that.
     */
    set = (BumpContext *) malloc(allocSize);
    if (set == NULL)
    {
        MemoryContextStats(TopMemoryContext);
        ereport(ERROR,
                (errcode(ERRCODE_OUT_OF_MEMORY),
                 errmsg("out of memory"),
                 errdetail("Failed while creating memory context \"%s\".",
                           name)));
    }
 
    /*
     * Avoid writing code that can fail between here and MemoryContextCreate;
     * we'd leak the header and initial block if we ereport in this stretch.
     */
    dlist_init(&set->blocks);
 
    /* Fill in the initial block's block header */
    block = KeeperBlock(set);
    /* determine the block size and initialize it */
    firstBlockSize = allocSize - MAXALIGN(sizeof(BumpContext));
    BumpBlockInit(set, block, firstBlockSize);
 
    /* add it to the doubly-linked list of blocks */
    dlist_push_head(&set->blocks, &block->node);
 
    /*
     * Fill in BumpContext-specific header fields.  The Asserts above should
     * ensure that these all fit inside a uint32.
     */
    set->initBlockSize = (uint32) initBlockSize;
    set->maxBlockSize = (uint32) maxBlockSize;
    set->nextBlockSize = (uint32) initBlockSize;
 
    /*
     * Compute the allocation chunk size limit for this context.
     *
     * Limit the maximum size a non-dedicated chunk can be so that we can fit
     * at least Bump_CHUNK_FRACTION of chunks this big onto the maximum sized
     * block.  We must further limit this value so that it's no more than
     * MEMORYCHUNK_MAX_VALUE.  We're unable to have non-external chunks larger
     * than that value as we store the chunk size in the MemoryChunk 'value'
     * field in the call to MemoryChunkSetHdrMask().
     */
    set->allocChunkLimit = Min(maxBlockSize, MEMORYCHUNK_MAX_VALUE);
    while ((Size) (set->allocChunkLimit + Bump_CHUNKHDRSZ) >
           (Size) ((Size) (maxBlockSize - Bump_BLOCKHDRSZ) / Bump_CHUNK_FRACTION))
        set->allocChunkLimit >>= 1;
 
    /* Finally, do the type-independent part of context creation */
    MemoryContextCreate((MemoryContext) set, T_BumpContext, MCTX_BUMP_ID,
                        parent, name);
 
    ((MemoryContext) set)->mem_allocated = allocSize;
 
    return (MemoryContext) set;
}
 
/*
 * BumpReset
 *      Frees all memory which is allocated in the given set.
 *
 * The code simply frees all the blocks in the context apart from the keeper
 * block.
 */
void
BumpReset(MemoryContext context)
{
    BumpContext *set = (BumpContext *) context;
    dlist_mutable_iter miter;
 
    Assert(BumpIsValid(set));
 
#ifdef MEMORY_CONTEXT_CHECKING
    /* Check for corruption and leaks before freeing */
    BumpCheck(context);
#endif
 
    dlist_foreach_modify(miter, &set->blocks)
    {
        BumpBlock  *block = dlist_container(BumpBlock, node, miter.cur);
 
        if (IsKeeperBlock(set, block))
            BumpBlockMarkEmpty(block);
        else
            BumpBlockFree(set, block);
    }
 
    /* Reset block size allocation sequence, too */
    set->nextBlockSize = set->initBlockSize;
 
    /* Ensure there is only 1 item in the dlist */
    Assert(!dlist_is_empty(&set->blocks));
    Assert(!dlist_has_next(&set->blocks, dlist_head_node(&set->blocks)));
}
 
/*
 * BumpDelete
 *      Free all memory which is allocated in the given context.
 */
void
BumpDelete(MemoryContext context)
{
    /* Reset to release all releasable BumpBlocks */
    BumpReset(context);
    /* And free the context header and keeper block */
    free(context);
}
 
/*
 * Helper for BumpAlloc() that allocates an entire block for the chunk.
 *
 * BumpAlloc()'s comment explains why this is separate.
 */
pg_noinline
static void *
BumpAllocLarge(MemoryContext context, Size size, int flags)
{
    BumpContext *set = (BumpContext *) context;
    BumpBlock  *block;
#ifdef MEMORY_CONTEXT_CHECKING
    MemoryChunk *chunk;
#endif
    Size        chunk_size;
    Size        required_size;
    Size        blksize;
 
    /* validate 'size' is within the limits for the given 'flags' */
    MemoryContextCheckSize(context, size, flags);
 
#ifdef MEMORY_CONTEXT_CHECKING
    /* ensure there's always space for the sentinel byte */
    chunk_size = MAXALIGN(size + 1);
#else
    chunk_size = MAXALIGN(size);
#endif
 
    required_size = chunk_size + Bump_CHUNKHDRSZ;
    blksize = required_size + Bump_BLOCKHDRSZ;
 
    block = (BumpBlock *) malloc(blksize);
    if (block == NULL)
        return NULL;
 
    context->mem_allocated += blksize;
 
    /* the block is completely full */
    block->freeptr = block->endptr = ((char *) block) + blksize;
 
#ifdef MEMORY_CONTEXT_CHECKING
    /* block with a single (used) chunk */
    block->context = set;
 
    chunk = (MemoryChunk *) (((char *) block) + Bump_BLOCKHDRSZ);
 
    /* mark the MemoryChunk as externally managed */
    MemoryChunkSetHdrMaskExternal(chunk, MCTX_BUMP_ID);
 
    chunk->requested_size = size;
    /* set mark to catch clobber of "unused" space */
    Assert(size < chunk_size);
    set_sentinel(MemoryChunkGetPointer(chunk), size);
#endif
#ifdef RANDOMIZE_ALLOCATED_MEMORY
    /* fill the allocated space with junk */
    randomize_mem((char *) MemoryChunkGetPointer(chunk), size);
#endif
 
    /*
     * Add the block to the tail of allocated blocks list.  The current block
     * is left at the head of the list as it may still have space for
     * non-large allocations.
     */
    dlist_push_tail(&set->blocks, &block->node);
 
#ifdef MEMORY_CONTEXT_CHECKING
    /* Ensure any padding bytes are marked NOACCESS. */
    VALGRIND_MAKE_MEM_NOACCESS((char *) MemoryChunkGetPointer(chunk) + size,
                               chunk_size - size);
 
    /* Disallow access to the chunk header. */
    VALGRIND_MAKE_MEM_NOACCESS(chunk, Bump_CHUNKHDRSZ);
 
    return MemoryChunkGetPointer(chunk);
#else
    return (void *) (((char *) block) + Bump_BLOCKHDRSZ);
#endif
}
 
/*
 * Small helper for allocating a new chunk from a chunk, to avoid duplicating
 * the code between BumpAlloc() and BumpAllocFromNewBlock().
 */
static inline void *
BumpAllocChunkFromBlock(MemoryContext context, BumpBlock *block, Size size,
                        Size chunk_size)
{
#ifdef MEMORY_CONTEXT_CHECKING
    MemoryChunk *chunk;
#else
    void       *ptr;
#endif
 
    /* validate we've been given a block with enough free space */
    Assert(block != NULL);
    Assert((block->endptr - block->freeptr) >= Bump_CHUNKHDRSZ + chunk_size);
 
#ifdef MEMORY_CONTEXT_CHECKING
    chunk = (MemoryChunk *) block->freeptr;
#else
    ptr = (void *) block->freeptr;
#endif
 
    /* point the freeptr beyond this chunk */
    block->freeptr += (Bump_CHUNKHDRSZ + chunk_size);
    Assert(block->freeptr <= block->endptr);
 
#ifdef MEMORY_CONTEXT_CHECKING
    /* Prepare to initialize the chunk header. */
    VALGRIND_MAKE_MEM_UNDEFINED(chunk, Bump_CHUNKHDRSZ);
 
    MemoryChunkSetHdrMask(chunk, block, chunk_size, MCTX_BUMP_ID);
    chunk->requested_size = size;
    /* set mark to catch clobber of "unused" space */
    Assert(size < chunk_size);
    set_sentinel(MemoryChunkGetPointer(chunk), size);
 
#ifdef RANDOMIZE_ALLOCATED_MEMORY
    /* fill the allocated space with junk */
    randomize_mem((char *) MemoryChunkGetPointer(chunk), size);
#endif
 
    /* Ensure any padding bytes are marked NOACCESS. */
    VALGRIND_MAKE_MEM_NOACCESS((char *) MemoryChunkGetPointer(chunk) + size,
                               chunk_size - size);
 
    /* Disallow access to the chunk header. */
    VALGRIND_MAKE_MEM_NOACCESS(chunk, Bump_CHUNKHDRSZ);
 
    return MemoryChunkGetPointer(chunk);
#else
    return ptr;
#endif                          /* MEMORY_CONTEXT_CHECKING */
}
 
/*
 * Helper for BumpAlloc() that allocates a new block and returns a chunk
 * allocated from it.
 *
 * BumpAlloc()'s comment explains why this is separate.
 */
pg_noinline
static void *
BumpAllocFromNewBlock(MemoryContext context, Size size, int flags,
                      Size chunk_size)
{
    BumpContext *set = (BumpContext *) context;
    BumpBlock  *block;
    Size        blksize;
    Size        required_size;
 
    /*
     * The first such block has size initBlockSize, and we double the space in
     * each succeeding block, but not more than maxBlockSize.
     */
    blksize = set->nextBlockSize;
    set->nextBlockSize <<= 1;
    if (set->nextBlockSize > set->maxBlockSize)
        set->nextBlockSize = set->maxBlockSize;
 
    /* we'll need space for the chunk, chunk hdr and block hdr */
    required_size = chunk_size + Bump_CHUNKHDRSZ + Bump_BLOCKHDRSZ;
    /* round the size up to the next power of 2 */
    if (blksize < required_size)
        blksize = pg_nextpower2_size_t(required_size);
 
    block = (BumpBlock *) malloc(blksize);
 
    if (block == NULL)
        return MemoryContextAllocationFailure(context, size, flags);
 
    context->mem_allocated += blksize;
 
    /* initialize the new block */
    BumpBlockInit(set, block, blksize);
 
    /* add it to the doubly-linked list of blocks */
    dlist_push_head(&set->blocks, &block->node);
 
    return BumpAllocChunkFromBlock(context, block, size, chunk_size);
}
 
/*
 * BumpAlloc
 *      Returns a pointer to allocated memory of given size or raises an ERROR
 *      on allocation failure, or returns NULL when flags contains
 *      MCXT_ALLOC_NO_OOM.
 *
 * No request may exceed:
 *      MAXALIGN_DOWN(SIZE_MAX) - Bump_BLOCKHDRSZ - Bump_CHUNKHDRSZ
 * All callers use a much-lower limit.
 *
 *
 * Note: when using valgrind, it doesn't matter how the returned allocation
 * is marked, as mcxt.c will set it to UNDEFINED.
 * This function should only contain the most common code paths.  Everything
 * else should be in pg_noinline helper functions, thus avoiding the overhead
 * of creating a stack frame for the common cases.  Allocating memory is often
 * a bottleneck in many workloads, so avoiding stack frame setup is
 * worthwhile.  Helper functions should always directly return the newly
 * allocated memory so that we can just return that address directly as a tail
 * call.
 */
void *
BumpAlloc(MemoryContext context, Size size, int flags)
{
    BumpContext *set = (BumpContext *) context;
    BumpBlock  *block;
    Size        chunk_size;
    Size        required_size;
 
    Assert(BumpIsValid(set));
 
#ifdef MEMORY_CONTEXT_CHECKING
    /* ensure there's always space for the sentinel byte */
    chunk_size = MAXALIGN(size + 1);
#else
    chunk_size = MAXALIGN(size);
#endif
 
    /*
     * If requested size exceeds maximum for chunks we hand the request off to
     * BumpAllocLarge().
     */
    if (chunk_size > set->allocChunkLimit)
        return BumpAllocLarge(context, size, flags);
 
    required_size = chunk_size + Bump_CHUNKHDRSZ;
 
    /*
     * Not an oversized chunk.  We try to first make use of the latest block,
     * but if there's not enough space in it we must allocate a new block.
     */
    block = dlist_container(BumpBlock, node, dlist_head_node(&set->blocks));
 
    if (BumpBlockFreeBytes(block) < required_size)
        return BumpAllocFromNewBlock(context, size, flags, chunk_size);
 
    /* The current block has space, so just allocate chunk there. */
    return BumpAllocChunkFromBlock(context, block, size, chunk_size);
}
 
/*
 * BumpBlockInit
 *      Initializes 'block' assuming 'blksize'.  Does not update the context's
 *      mem_allocated field.
 */
static inline void
BumpBlockInit(BumpContext *context, BumpBlock *block, Size blksize)
{
#ifdef MEMORY_CONTEXT_CHECKING
    block->context = context;
#endif
    block->freeptr = ((char *) block) + Bump_BLOCKHDRSZ;
    block->endptr = ((char *) block) + blksize;
 
    /* Mark unallocated space NOACCESS. */
    VALGRIND_MAKE_MEM_NOACCESS(block->freeptr, blksize - Bump_BLOCKHDRSZ);
}
 
/*
 * BumpBlockIsEmpty
 *      Returns true iff 'block' contains no chunks
 */
static inline bool
BumpBlockIsEmpty(BumpBlock *block)
{
    /* it's empty if the freeptr has not moved */
    return (block->freeptr == ((char *) block + Bump_BLOCKHDRSZ));
}
 
/*
 * BumpBlockMarkEmpty
 *      Set a block as empty.  Does not free the block.
 */
static inline void
BumpBlockMarkEmpty(BumpBlock *block)
{
#if defined(USE_VALGRIND) || defined(CLOBBER_FREED_MEMORY)
    char       *datastart = ((char *) block) + Bump_BLOCKHDRSZ;
#endif
 
#ifdef CLOBBER_FREED_MEMORY
    wipe_mem(datastart, block->freeptr - datastart);
#else
    /* wipe_mem() would have done this */
    VALGRIND_MAKE_MEM_NOACCESS(datastart, block->freeptr - datastart);
#endif
 
    /* Reset the block, but don't return it to malloc */
    block->freeptr = ((char *) block) + Bump_BLOCKHDRSZ;
}
 
/*
 * BumpBlockFreeBytes
 *      Returns the number of bytes free in 'block'
 */
static inline Size
BumpBlockFreeBytes(BumpBlock *block)
{
    return (block->endptr - block->freeptr);
}
 
/*
 * BumpBlockFree
 *      Remove 'block' from 'set' and release the memory consumed by it.
 */
static inline void
BumpBlockFree(BumpContext *set, BumpBlock *block)
{
    /* Make sure nobody tries to free the keeper block */
    Assert(!IsKeeperBlock(set, block));
 
    /* release the block from the list of blocks */
    dlist_delete(&block->node);
 
    ((MemoryContext) set)->mem_allocated -= ((char *) block->endptr - (char *) block);
 
#ifdef CLOBBER_FREED_MEMORY
    wipe_mem(block, ((char *) block->endptr - (char *) block));
#endif
 
    free(block);
}
 
/*
 * BumpFree
 *      Unsupported.
 */
void
BumpFree(void *pointer)
{
    elog(ERROR, "%s is not supported by the bump memory allocator", "pfree");
}
 
/*
 * BumpRealloc
 *      Unsupported.
 */
void *
BumpRealloc(void *pointer, Size size, int flags)
{
    elog(ERROR, "%s is not supported by the bump memory allocator", "realloc");
    return NULL;                /* keep compiler quiet */
}
 
/*
 * BumpGetChunkContext
 *      Unsupported.
 */
MemoryContext
BumpGetChunkContext(void *pointer)
{
    elog(ERROR, "%s is not supported by the bump memory allocator", "GetMemoryChunkContext");
    return NULL;                /* keep compiler quiet */
}
 
/*
 * BumpGetChunkSpace
 *      Unsupported.
 */
Size
BumpGetChunkSpace(void *pointer)
{
    elog(ERROR, "%s is not supported by the bump memory allocator", "GetMemoryChunkSpace");
    return 0;                   /* keep compiler quiet */
}
 
/*
 * BumpIsEmpty
 *      Is a BumpContext empty of any allocated space?
 */
bool
BumpIsEmpty(MemoryContext context)
{
    BumpContext *set = (BumpContext *) context;
    dlist_iter  iter;
 
    Assert(BumpIsValid(set));
 
    dlist_foreach(iter, &set->blocks)
    {
        BumpBlock  *block = dlist_container(BumpBlock, node, iter.cur);
 
        if (!BumpBlockIsEmpty(block))
            return false;
    }
 
    return true;
}
 
/*
 * BumpStats
 *      Compute stats about memory consumption of a Bump context.
 *
 * printfunc: if not NULL, pass a human-readable stats string to this.
 * passthru: pass this pointer through to printfunc.
 * totals: if not NULL, add stats about this context into *totals.
 * print_to_stderr: print stats to stderr if true, elog otherwise.
 */
void
BumpStats(MemoryContext context, MemoryStatsPrintFunc printfunc,
          void *passthru, MemoryContextCounters *totals, bool print_to_stderr)
{
    BumpContext *set = (BumpContext *) context;
    Size        nblocks = 0;
    Size        totalspace = 0;
    Size        freespace = 0;
    dlist_iter  iter;
 
    Assert(BumpIsValid(set));
 
    dlist_foreach(iter, &set->blocks)
    {
        BumpBlock  *block = dlist_container(BumpBlock, node, iter.cur);
 
        nblocks++;
        totalspace += (block->endptr - (char *) block);
        freespace += (block->endptr - block->freeptr);
    }
 
    if (printfunc)
    {
        char        stats_string[200];
 
        snprintf(stats_string, sizeof(stats_string),
                 "%zu total in %zu blocks; %zu free; %zu used",
                 totalspace, nblocks, freespace, totalspace - freespace);
        printfunc(context, passthru, stats_string, print_to_stderr);
    }
 
    if (totals)
    {
        totals->nblocks += nblocks;
        totals->totalspace += totalspace;
        totals->freespace += freespace;
    }
}
 
 
#ifdef MEMORY_CONTEXT_CHECKING
 
/*
 * BumpCheck
 *      Walk through chunks and check consistency of memory.
 *
 * NOTE: report errors as WARNING, *not* ERROR or FATAL.  Otherwise you'll
 * find yourself in an infinite loop when trouble occurs, because this
 * routine will be entered again when elog cleanup tries to release memory!
 */
void
BumpCheck(MemoryContext context)
{
    BumpContext *bump = (BumpContext *) context;
    const char *name = context->name;
    dlist_iter  iter;
    Size        total_allocated = 0;
 
    /* walk all blocks in this context */
    dlist_foreach(iter, &bump->blocks)
    {
        BumpBlock  *block = dlist_container(BumpBlock, node, iter.cur);
        int         nchunks;
        char       *ptr;
        bool        has_external_chunk = false;
 
        if (IsKeeperBlock(bump, block))
            total_allocated += block->endptr - (char *) bump;
        else
            total_allocated += block->endptr - (char *) block;
 
        /* check block belongs to the correct context */
        if (block->context != bump)
            elog(WARNING, "problem in Bump %s: bogus context link in block %p",
                 name, block);
 
        /* now walk through the chunks and count them */
        nchunks = 0;
        ptr = ((char *) block) + Bump_BLOCKHDRSZ;
 
        while (ptr < block->freeptr)
        {
            MemoryChunk *chunk = (MemoryChunk *) ptr;
            BumpBlock  *chunkblock;
            Size        chunksize;
 
            /* allow access to the chunk header */
            VALGRIND_MAKE_MEM_DEFINED(chunk, Bump_CHUNKHDRSZ);
 
            if (MemoryChunkIsExternal(chunk))
            {
                chunkblock = ExternalChunkGetBlock(chunk);
                chunksize = block->endptr - (char *) MemoryChunkGetPointer(chunk);
                has_external_chunk = true;
            }
            else
            {
                chunkblock = MemoryChunkGetBlock(chunk);
                chunksize = MemoryChunkGetValue(chunk);
            }
 
            /* move to the next chunk */
            ptr += (chunksize + Bump_CHUNKHDRSZ);
 
            nchunks += 1;
 
            /* chunks have both block and context pointers, so check both */
            if (chunkblock != block)
                elog(WARNING, "problem in Bump %s: bogus block link in block %p, chunk %p",
                     name, block, chunk);
        }
 
        if (has_external_chunk && nchunks > 1)
            elog(WARNING, "problem in Bump %s: external chunk on non-dedicated block %p",
                 name, block);
 
    }
 
    Assert(total_allocated == context->mem_allocated);
}
 
#endif                          /* MEMORY_CONTEXT_CHECKING */